Method for recovering a liquid-phase oxidation catalyst for preparation of terephthalic acid

Claim 1

A method for recovering a heavy metal oxidation catalyst comprising a metal selected from cobalt and manganese from the residue of the reaction mother liquor containing the heavy metal oxidation catalyst, organic impurities and a small amount of heavy metal impurities, said residue being obtained by removing a solvent selected from a lower aliphatic monocarboxylic acid from the reaction mother liquor remaining after recovering terephthalic acid from the oxidation reaction product obtained in the process for producing terephthalic acid by subjecting an alkylbenzene to a liquid-phase oxidation with oxygen or an oxygen-containing gas in the presence of the heavy metal oxidation catalyst using said solvent, which comprises: A. stirring an aqueous dispersion of said residue in the presence of a sulfur compound selected from the group consisting of hydrogen sulfide, sodium sulfide, sodium hydrosulfide, potassium hydrosulfide and ammonium hydrosulfide while contacting a gas containing molecular oxygen with said dispersion wherein the amount of the sulfur compound is not more than about 1% by weight calculated as sulfur based on the weight of the heavy metal component of the catalyst and the amount of water in the aqueous dispersion is about 0.5 to 6 times of the weight of the residue, thereby to extract said heavy metal oxidation catalyst into said aqueous phase, and to precipitate organic impurities and heavy metal impurities, B. subjecting said aqueous dispersion to a solid-liquid separation at a temperature of not more than about 50°C to separate the solid organic impurities and heavy metal impurities and obtain an aqueous solution containing the oxidation catalyst, C. adding the aqueous solution containing the oxidation catalyst to an alkali metal or ammonium carbonate or an aqueous solution of an alkali metal or ammonium carbonate while maintaining the temperature of the system at about 26°C to 70°C, to form a solution containing a precipitate of a carbonate of the heavy metal catalyst, and D. subjecting the solution containing the precipitate of the carbonate of the heavy metal catalyst to a solid-liquid separation to recover the heavy metal catalyst as a carbonate precipitate.

Claim 2

A method for recovering a heavy metal oxidation catalyst comprising a metal selected from cobalt and manganese from the residue of the reaction mother liquor containing the heavy metal oxidation catalyst, organic impurities and a small amount of heavy metal impurities, said residue being obtained by removing a solvent selected from a lower aliphatic monocarboxylic acid from the reaction mother liquor remaining after recovering terephthalic acid from the oxidation reaction product obtained in the process for producing terephthalic acid by subjecting an alkylbenzene to a liquid-phase oxidation with oxygen or an oxygen-containing gas in the presence of the heavy metal oxidation catalyst using said solvent, which comprises: A. stirring an aqueous dispersion of said residue in the presence of a sulfur compound selected from the group consisting of hydrogen sulfide, sodium sulfide, sodium hydrosulfide, potassium hydrosulfide and ammonium hydrosulfide while contacting a gas containing molecular oxygen with said dispersion wherein the amount of the sulfur compound is not more than about 1% by weight calculated as sulfur based on the weight of the heavy metal component of the catalyst and the amount of water in the aqueous dispersion is about 0.5 to 6 times of the weight of the residue, thereby to extract said heavy metal oxidation catalyst into said aqueous phase, and to precipitate organic impurities and heavy metal impurities, B. subjecting said aqueous dispersion to a solid-liquid separation at a temperature of not more than about 50°C to separate the solid organic impurities and heavy metal impurities and obtain an aqueous solution containing the oxidation catalyst, C. adding the aqueous solution containing the oxidation catalyst to an alkali metal or ammonium carbonate or an aqueous solution of an alkali metal or ammonium carbonate while maintaining the temperature of the system at about 26°C to 70°C, to form a solution containing a precipitate of a carbonate of the heavy metal catalyst, and D. subjecting the solution containing the precipitate of the carbonate of the heavy metal catalyst to a solid-liquid separation to recover the heavy metal catalyst as a carbonate precipitate.